An arrangement in which the exhaust gas of a diesel engine is guided to an evaporator so as to heat water and generate steam, and the pressure energy and the thermal energy of this steam are used to operate an expander and generate mechanical energy is known from Japanese Patent Application Laid-open No. 60-64101. In this arrangement the flow rate of the exhaust gas is used as one of the parameters with which control is carried out in order to make the temperature of the steam generated in the evaporator coincide with a target steam temperature, and this exhaust gas flow rate is estimated based on the position of a fuel rack of the engine.
Furthermore, the present applicant has proposed in Japanese Patent Application No. 2000-311680 an arrangement in which the energy of exhaust gas is calculated based on the intake negative pressure and the rotational speed of an engine, and an amount of feedforward for controlling the amount of water supplied to an evaporator is calculated based on this exhaust gas energy.
However, in the arrangement disclosed in Japanese Patent Application Laid-open No. 60-64101, due to a delay in pumping fuel and a mechanical delay in a governor mechanism, the amount of fuel supplied does not respond quickly to a change in the engine rotational speed, and it is difficult to estimate with high precision the flow rate of the exhaust gas when the output of the engine changes.
Moreover, in the arrangement proposed in Japanese Patent Application No. 2000-311680, since the intake negative pressure of the engine is used when calculating the feedforward value for controlling the amount of water supplied, it is necessary to change the parameters for calculating the amount of water supplied in accordance with engine specifications (displacement, exhaust port shape, combustion chamber shape).